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W222 S63 AMG M157 Catless Downpipes – Premium Stainless Steel High-Flow Set
W222 S63 AMG M157 Catless Downpipes – Premium Stainless Steel High-Flow Set
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High-flow catless downpipes for the 2014–2017 Mercedes-AMG S63 (W222) with the M157 5.5L BiTurbo V8. They replace the factory primary catalytic converters — the single largest restriction in the system — for quicker turbo spool, sharper mid-range response, and a deeper AMG note. Back-purged TIG-welded 304 stainless steel, 2.71″ primaries tapering to 2.63″, direct bolt-on with no cutting. Supplied as a complete left and right set with V-band clamps, mounting hardware and gaskets. In US stock and shipped next business day.
Driving an E63 or CLS63? Those cars run the same M157 engine, but downpipes are chassis-specific and this set will not fit — E63 / CLS63 RWD (2012–2013) → · E63 / CLS63 4MATIC →
Key Features & Benefits
- 2.71″ Primaries Tapering To 2.63″ — sized to what the S63 actually flows, not to a round number. The taper accelerates exhaust gas through the section rather than letting it stall in an oversized pipe, which is what protects mid-range torque and turbo response
- TIG-Welded 304 Stainless Steel — back-purged welds throughout for long-term reliability under repeated heat cycling
- Complete Bolt-On Set — left and right downpipes, V-band clamps, mounting hardware and gaskets included. No cutting or modification; installs in 2–3 hours with professional installation strongly recommended, and re-check for leaks after the first heat cycle
- Reduced Exhaust Backpressure — faster turbo spool and a deeper AMG V8 tone, with crackle on overrun once tuned
Will downpipes alone add power?
A little. Nothing like the numbers you'll see advertised.
Your ECU targets a set boost level and holds it with the wastegate. Lower the backpressure and it doesn't raise that target — it just reaches the same number with the gate cracked further open. Fuel is metered to measured airmass to hold a target air-fuel ratio, so if airmass doesn't change, fuelling doesn't change, and neither does power. You don't make more power without burning more fuel, and the ECU decides how much fuel it burns.
There are two places you do gain on a stock calibration. At the top of the pull the wastegate is already shut and the turbos are at their limit — there's no regulation left, so less restriction means genuinely more airflow and the ECU fuels it. And lower exhaust gas temperatures mean less timing pulled on a knock-limited engine. Together that's a handful of horsepower, mostly at high RPM.
What you'll feel is much bigger than what you'll measure. Boost arrives sooner, so the car is quicker to respond and quicker between gears — which is why owners often report large gains from downpipes alone. That's turbo response, not output.
The flow becomes power when the calibration does. A tune raises the boost target and fuels it. Any large figure quoted for "downpipes alone" was almost certainly measured on a tuned car — a real number with a misleading label.
Complete the Stage 2 Build
These downpipes are the hardware half of a Stage 2 M157. The tune is what turns them loose — it lets the ECU take advantage of the extra flow, and it clears the check-engine light the catless design will otherwise set.
What Else Owners Add At The Same Time
Downpipes free up the exhaust side. These address the intake side, the install itself, and under-hood heat — worth doing together while the car is already on the lift.
- Intake: M157 intake spacer kit and K&N high-flow air filters
- Install: 24″ O₂ sensor extension harness — catless pipes reposition the sensor bungs and the factory leads often will not reach comfortably
- Heat: M157 turbo blankets — keeps radiant heat off surrounding components in the tight W222 engine bay
Compatibility
| Chassis | Years | Models |
|---|---|---|
| W222 Sedan | 2014–2017 | Mercedes-AMG S63 |
All fitments above use the M157 5.5L BiTurbo V8. If your car is on that list, these bolt straight on with no cutting or fabrication.
Warranty, Shipping & Returns
- 12-month structural warranty — covers welds, flanges, and structural integrity under normal street use
- Free U.S. shipping with tracking, shipped next business day from US stock
- 30-day returns — unused and in original packaging. See full return policy →
Frequently Asked Questions
Why 2.71″ and not 3 inches?
A downpipe sized past what the engine actually flows drops exhaust gas velocity, and velocity is what carries mid-range torque and turbo response. Each downpipe is sized to the engine it fits rather than to one number applied across every platform. The S63 set runs 2.71″ primaries tapering to 2.63″ — nobody specifies to a hundredth of an inch by accident. The taper accelerates gas through the section instead of letting it stall, which is exactly what a generic 3″ pipe sold across four different engine families gives up in the mid-range.
Will these throw a check engine light?
Likely, on an untuned car. Removing the cats means the downstream O₂ sensors read differently than the ECU expects. A calibration resolves it properly — we do not recommend defeat devices.
Do these require a tune?
They fit and run fine on a stock car, and the sharper throttle response is immediate. The power arrives with the calibration. A tune is highly recommended for maximum performance and to clear fault codes.
How much power can I expect?
We do not publish a downpipe-only figure for this platform because we have not dyno'd one, and we will not repeat a number we cannot stand behind. What these change on a stock calibration is response rather than output — see the explanation above. The power comes with the tune, and the exact figure depends on your calibration, fuel grade and supporting modifications.
Do I need the O₂ sensor extension harness?
Often, yes. A catless downpipe repositions the sensor bungs relative to the factory pipe, and the original leads may not reach comfortably. A 24″ extension avoids stretching or splicing the harness — a small part that prevents a stalled install.
Are these street legal?
No. These delete the primary catalytic converter. They hold no CARB Executive Order, are not 50-state legal, and are not legal to install on a vehicle registered or operated on public roads in the United States. Sold for closed-course competition and off-road use only — see the emissions notice at the top of this page.
Is there a warranty?
Yes — a 12-month structural warranty, with guaranteed fitment on every model listed above.
Off road use only. Not legal for use on emissions-controlled vehicles or public roads.
